Heat pumps or reverse cycle refrigerating systems having two coils for interchangeably acting as the evaporator and the condenser are old in the art. So is the use of such systems for cooling and dehumidifying air and accumulating frost on one cycle, and for defrosting the frost on a second cycle. It is also believed to be old to position both coils in the same air stream, thereby securing the desired cooling and humidifying effect from one coil acting as the evaporator while simultaneously warming and "reheating" the airstream from the heat discharged from the other coil acting as the condenser.
When the dehumidifier is used to dehumidify a cold environment. That is, when the dehumidifier is employed to dehumidify air where the desired temperature of the dehumidified environment and the source of air entering the dehumidifier, is 55 F. or less, the temperature of the refrigerant in the cooling/dehumidifying coil will be less than 32 F., the freezing point of water. Such conditions are common in indoor ice skating rinks and similar environments.
Under these operating conditions, water condensed from the air as a necessary function of the dehumidifying process, collects on the cooling/dehumidifying coil in the form of frost. This frost accumulates on surfaces of the fins and tubes of the cooling/dehumidifying coil, the evaporator.
As the frost accumulates on the coil fins and tubes, it gradually reduces the coil area available for air flow, thereby reducing the flow of air through the coil and increasing the fan motor power. In addition the frost accumulation acts as insulation between the air-to-be-dehumidified and the tubes and fins of the coil. This makes the coil a much less effective heat transfer device and gradually reduces the dehumidification effect of the evaporator coil as the air flow over the coil becomes increasingly restricted.
The evaporator coil, having accumulated a quantity of frost deemed to be excessive, must therefore be defrosted so that it, after the defrost, can continue to operate efficiently, that is, with the high, unrestricted original air flow and with the high original heat transfer capacity, un-reduced by any insulating frost formation.
Newer, unobvious technology, described in co-pending patent application having Ser. No. 08/855,441 and titled "Improved Dehumidifier", discloses the use of a damper allowing and preventing air flow over the one coil which acts as the cooling and dehumidifying coil, whereby air is allowed to flow over the coil while it is refrigerating and dehumidifying, and prevented from flowing over the coil while it is heating and defrosting. With the air flow over the defrosting coil stopped, moisture rising from the warmed coil during defrosting is prevented from being carried away in the air stream which would, at least in part, defeat the total dehumidifying effort.
While the above described system is perfectly workable and achieves its objective, improvements are possible. This invention is intended to describe the improvements, and the benefits which arise from their use.